1. Field of the Invention
The present invention relates to an optical coupling semiconductor apparatus having a light-emitting device and a light-receiving device which are sealed by plastic molding, and to a method for manufacturing the same.
2. Description of the Related Art
Among prior art semiconductor apparatus of this type, there is known a semiconductor apparatus with a double-layer molding seal as shown in FIG. 12, for example. As shown in FIG. 12, light-emitting device 103 and light-receiving device 104 are mounted on headers 101a and 102a, respectively, of previously bent lead frames 101 and 102 of a metal material, such as Cu alloy or Fe alloy, by connecting them to respective headers with an electrically conductive paste, such as Ag paste, (called xe2x80x9cdie bondingxe2x80x9d). These devices 103 and 104 are connected to the corresponding lead frames by means of wires (called xe2x80x9cwire bondingxe2x80x9d).
The light-emitting device 103 is coated with a silicone resin (called xe2x80x9cprecoatxe2x80x9d) to relieve stress, and the light-emitting device 103 and light-receiving device 104 are positioned to face each other by spot welding of the lead frames 101 and 102 or using a loading frame set. Further, an inner package 105 serving as an optical path between the light-emitting device 103 and the light-receiving device 104 is formed by primary transfer molding using a light-transmissive epoxy resin, followed by removal of resin burr resulting from leakage of excess resin.
Subsequently, an outer package 106 is formed by secondary transfer molding using a lightproof epoxy resin to prevent penetration of external disturbing light and leakage of internal light to the outside. Then, the lead frames 101 and 102 are plated for lead finishing. Further, an auxiliary lead portion, which plays two roles, i.e., tying and supporting of the lead frames 101 and 102 and prevention of resin leakage during transfer molding, is cut away (called xe2x80x9ctie bar cuttingxe2x80x9d), and exposed lead portions of the lead frames extending from the outer package 106 are formed into external terminals (called xe2x80x9cformingxe2x80x9d).
In such a prior art apparatus, light emitted from the light-emitting device 103 advances straight to the light-receiving device 104.
A reflection-type photocoupler disclosed in, for example, Japanese Unexamined Patent Publication JP-A 11-17212 (1999) is constructed as shown in FIG. 13. Specifically, this photocoupler is constructed by: mounting light-emitting device 203 and light-receiving device 204 on lead frames 201 and 202, respectively; covering the light-emitting device 203 and light-receiving device 204 with a silicone resin 205 to define an optical path between the light-emitting device 203 and the light-receiving device 204 (called xe2x80x9cdockingxe2x80x9d); forming an outer package 206 by transfer molding using a lightproof epoxy resin; and performing finish-plating of the lead frames 201 and 202, tie bar cutting, forming and the like.
In such a prior art photocoupler, as shown in FIG. 14, light emitted from the light-emitting device 203 is reflected by the interface defined between the silicone resin 205 and the outer package 206 and then reaches the light-receiving device 204.
With respect to the prior art apparatus shown in FIG. 12, however, the headers 101a and 102a necessarily face each other because the light-emitting device 103 and the light-receiving device 104 are disposed facing each other. When the headers 101a and 102a in this state are sealed with the epoxy resin that will serve as the inner package 105, a floating capacity (electrostatic capacity) results between the headers 101a and 102a. In this case, when the potential between the light-emitting device 103 and the light-receiving device 104 varies steeply, displacement current flows through the light-receiving device 104 and, hence, the output of the light-receiving device 104 is apparently changed, which causes a malfunction to occur.
With respect to the prior art photocoupler shown in FIG. 13, on the other hand, the light-emitting device 203 and the light-receiving device 204 do not face each other and, hence, the lead frames 201 and 202 do not face each other either. Accordingly, a very low floating capacity results. However, since light emitted from the light-emitting device 203 is dispersed within the silicone resin 205 and repeatedly reflected by the interface between the silicone resin 205 and the outer package 206, the proportion of light absorbed by the interface or the like before light reaches the light-receiving device 204 is high, which raises a problem that a decrease or fluctuations in the efficiency of light transmission from the light-emitting device 203 to the light-receiving device 204 occur. In addition, since the silicone resin 205 is large in volume, possible thermal expansion thereof is likely to cause the outer package 206 to crack, thus resulting in an inconvenience such as penetration or leakage of light.
The invention has been made in view of the foregoing problems involved in the prior art, and accordingly, it is an object of the invention to provide an optical coupling semiconductor apparatus which is capable of raising and stabilizing the efficiency of light transmission from the light-emitting device to the light-receiving device and to provide a method for manufacturing the same.
According to the invention, there is provided an optical coupling semiconductor apparatus comprising:
a light-emitting device;
a light-receiving device;
lead frames carrying the light-emitting device and the light-receiving device, respectively, at locations spaced apart from each other; and
a light-transmissive resin projection having a longitudinally extending tapered vertex portion, the projection functioning as an optical path extending between the light-emitting device and the light-receiving device, having a nearly constant height, reflecting light emitted from the light-emitting device to gather the light to the vertex portion, and guiding the light thus gathered to the light-receiving device.
According to the invention, the light-transimissive resin projection having a constant height functions as an optical path extending between the light-emitting device and the light-receiving device, reflects light emitted from the light-emitting device to gather the light to the vertex portion thereof, and guides the light to the light-receiving device. Accordingly, light from the light-emitting device is guided to the light-receiving device without being dispersed. For this reason, the efficiency of light transmission from the light-emitting device to the light-receiving device is high and is stabilized.
In the invention, it is preferable that the light-emitting device and the light-receiving device have a light-emitting face and a light-receiving face, respectively, which are located on substantially the same reference plane.
According to the invention, it is possible to ensure a higher light transmission efficiency and minimize the floating capacity between the lead frames carrying the light-emitting device and the light-receiving device, respectively.
In the invention, it is preferable that the light-transmissive resin projection has a sectional configuration with the vertex portion and two sides defining the vertex portion.
According to the invention, the light-transmissive resin projection of such a sectional configuration is capable of reflecting light emitted from the light-emitting device at two inner wall surfaces facing each other to gather the light to the vertex portion, and guiding the light thus gathered.
In the invention, it is preferable that the light-transmissive resin projection is formed of an epoxy resin which is capable of setting through cationic polymerization.
According to the invention, this epoxy resin is preferred in terms of humidity resistance.
Further, in the invention, it is preferable that the light-transmissive resin projection is dome-shaped at a location in a vicinity of the light-receiving device to converge light at the light-receiving device.
According to the invention, the efficiency of light transmission to the light-receiving device is further raised.
In the invention, it is preferable that a distance l between the light-emitting device and the light-receiving device and a height L of the light-transmissive resin projection are set to satisfy the following relation:
lxe2x89xa7L. 
According to the invention, the distance l between the light-emitting device and the light-receiving device and the height L of the light-transmissive resin projection are set to satisfy the relation: lxe2x89xa7L, for light to be gathered without being dispersed.
Further, in the invention, it is preferable that the light-transmissive resin projection has a width larger than a width of a light-emitting area of the light-emitting device and a width of a light-receiving area of the light-receiving device.
According to the invention, the light-transmissive resin projection is capable of efficiently receiving light from the light-emitting device and guiding it to the light-receiving device, thereby ensuring higher light transmission efficiency.
In the invention, it is preferable that the light-transmissive resin projection has opposite ends located as superposed on the light-emitting device and the light-receiving device, respectively.
Alternatively, in the invention, it is preferable that the light-transmissive resin projection has one end adjoining the light-receiving device.
According to the invention, the light-transmissive resin projection has an end superposed on or adjoining the light-emitting device or the light-receiving device and, hence, light from the light-emitting device is guided to the light-receiving device before it is dispersed, whereby higher light transmission efficiency is ensured.
In the invention, it is preferable that the light-emitting device is shaped into a prism having at least two side walls oriented toward the light-receiving device.
According to the invention, if the light-emitting device is in the form of a quadratic prism, the amount of light received by the light-receiving device from the light-emitting device having two side walls oriented toward the light-receiving device increases by {square root over (2)} times at maximum as compared with the case where the light-emitting device has only one side wall oriented toward the light-receiving device.
According to the invention, there is also provided a method for manufacturing an optical coupling semiconductor apparatus, comprising the steps of: mounting a light-emitting device and a light-receiving device on respective lead frames and connecting the light-emitting device and the light-receiving device to the corresponding lead frames by die bonding or wire bonding; forming a light-transmissive resin projection having a longitudinally extending tapered vertex portion and a substantially constant height, the resin projection functioning as an optical path between the light-emitting device and the light-receiving device; and sealing the light-emitting device, the light-receiving device and the light-transmissive resin projection with a lightproof resin.
In the invention, it is preferable that the lightproof resin contains a flame-retardant resin which is white-colored and has an increased light reflectivity at least at a location in a vicinity of an interface with the light-transmissive resin projection.
According to the invention, such a lightproof resin raises the light reflectivity at the interface with the light-transmissive resin projection while ensuring higher light transmission efficiency.